This disclosure relates to a method for closed-loop control of the surface temperature of a glow plug.
In known methods, the electrical resistance of the glow plug is normally used as a control variable. The electrical resistance is calculated from continuously measured values of the heating current and of the electrical voltage. The electrical resistance is compared with a target value of the resistance, which is established from a predefined target temperature by means of a temperature/resistance characteristic curve. Instead of establishing a target value of the resistance from a target temperature, an actual value of the temperature can of course also be established from an actual value of the resistance and compared with the target temperature. Both approaches of closed-loop control are equivalent and are each based on a calculation rule that assigns a value of the surface temperature to a value pair formed of an actual value of the heating current and an actual value of the voltage.
The quality of the temperature control achieved in this way with known methods is poor, however. This is true in particular for ceramic glow plugs.